Optical fiber having scintillation quencher, a radiation sensor and a radiation detection apparatus including the optical fiber and a method of making and using the same

ABSTRACT

An optical fiber can include a polymer and a scintillation quencher. The optical fiber can be a member of a radiation sensor or radiation detecting system. The scintillation quencher can include a UV-absorber or a scintillation resistant material. In one embodiment, the radiation sensor includes a scintillator that is capable of generating a first radiation having a wavelength of at least about 420 nm; and a scintillation quencher is capable of absorbing a second radiation having a wavelength of less than about 420 nm. The optical fiber including a scintillation quencher provides for a method to detect neutrons in a radiation detecting system.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of and claims priority under 35U.S.C. §120 to U.S. patent application Ser. No. 13/536,744, filed Jun.28, 2012, entitled “Optical Fiber having Scintillation Quencher, aRadiation Sensor and a Radiation Detection Apparatus including theOptical Fiber and a Method of Making and Using the Same,” by Michael R.Kusner, which claims priority under 35 U.S.C. §119(e) to U.S.Provisional Patent Application No. 61/503,239 entitled “Optical Fiberhaving Scintillation Quencher, a Radiation Sensor and a RadiationDetection Apparatus including the Optical Fiber and a Method of Makingand Using the Same,” by Michael R. Kusner, filed Jun. 30, 2011, which isassigned to the current assignee hereof and incorporated herein byreference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure is directed to optical fibers, radiation sensorsand radiation detection apparatuses and methods of using the same, andmore particularly to optical fibers, radiation sensors and radiationdetection apparatuses including the optical fibers, and methods ofmaking and using the foregoing.

BACKGROUND

A radiation detector can include a plastic scintillator, such asalternating layers of wavelength shifting fibers and phosphorescentmaterials. The layers of phosphorescent material can be BC-704™-brandneutron sensing phosphorescent layers available from Saint-GobainCrystals of Hiram, Ohio, USA. Conventional neutron detection usingsolid-state scintillators typically rely on the optical coupling of aneutron-sensing scintillator material composite to a flat window of aphotosensor. The industry demands further improvements of neutrondetection in view of these detriments.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example and are not limited in theaccompanying figures.

FIG. 1 includes a schematic depiction of a radiation detection apparatusin accordance with an embodiment.

FIG. 2 includes an illustration of a cross-sectional view of a portionof a radiation sensor.

FIG. 3 includes an illustration of an exemplary application using aneutron detector.

FIG. 4 includes a depiction of pulse shape discrimination spectra for aneutron source when using radiation detection systems with and without ascintillation quencher.

FIG. 5 includes a depiction of pulse shape discrimination spectra for aneutron source with using radiation detecting systems with and without ascintillation quencher, when such radiation detecting systems areexposed to a significant gamma radiation field.

Skilled artisans appreciate that elements in the figures are illustratedfor simplicity and clarity and have not necessarily been drawn to scale.For example, the dimensions of some of the elements in the figures maybe exaggerated relative to other elements to help to improveunderstanding of embodiments of the invention.

DETAILED DESCRIPTION

The following description in combination with the figures is provided toassist in understanding the teachings disclosed herein. The followingdiscussion will focus on specific implementations and embodiments of theteachings. This focus is provided to assist in describing the teachingsand should not be interpreted as a limitation on the scope orapplicability of the teachings.

The term “corresponding radiation detecting system” is intended to meana radiation detecting system that is substantially identical and usedunder substantially the same conditions as a radiation detecting systemwith a scintillation quencher, except that the corresponding radiationdetecting system does not have the scintillation quencher within amedium used to transmit scintillation light through at least a portionof a radiation sensor towards a photosensor. For example, the radiationdetecting system with the scintillation quencher and the correspondingradiation detecting system may have substantially the same composition,thickness, and number of phosphor layers, and have substantially theoptical media, including substantially the same form (for example,optical fibers, an optical transmission sheet, or the like), number ofoptical media layers, and, except for the scintillation quencher,substantially the same composition.

The terms “comprises,” “comprising,” “includes,” “including,” “has,”“having,” or any other variation thereof, are intended to cover anon-exclusive inclusion. For example, a process, method, article, orapparatus that comprises a list of features is not necessarily limitedonly to those features but may include other features not expresslylisted or inherent to such process, method, article, or apparatus.Further, unless expressly stated to the contrary, “or” refers to aninclusive-or and not to an exclusive-or. For example, a condition A or Bis satisfied by any one of the following: A is true (or present) and Bis false (or not present), A is false (or not present) and B is true (orpresent), and both A and B are true (or present).

The use of “a” or “an” is employed to describe elements and componentsdescribed herein. This is done merely for convenience and to give ageneral sense of the scope of the invention. This description should beread to include one or at least one and the singular also includes theplural, or vice versa, unless it is clear that it is meant otherwise.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. The materials, methods, andexamples are illustrative only and not intended to be limiting. To theextent not described herein, many details regarding specific materialsand processing acts are conventional and may be found in textbooks andother sources within the scintillation and radiation detection arts.

Optical fibers as used in some radiation sensors or radiation detectingsystems can include a material that quenches undesired scintillation.Such a material can significantly reduce the likelihood of undesiredscintillation from particular materials or at particular wavelengths.Alternatively, such a material can quench undesired scintillation byabsorbing undesired scintillation radiation that is generated in theoptical fiber. The material is chosen to quench undesired scintillationwithout affecting any desired radiation that is transmitted along theoptical fiber.

FIG. 1 includes an illustration of an embodiment of a radiationdetection apparatus 10. In the embodiment illustrated, the radiationdetection apparatus 10 includes a radiation sensor 12 and photosensors16 and 17 that are optically coupled to the radiation sensor 12, whichhas a corresponding radiation sensing region 14. The radiation sensor 12can have many different shapes. Each or both of the photosensors 16 and17 can be in the form of a photomultiplier tube (PMT), asemiconductor-based photomultiplier, an avalanche photodiode, or ahybrid photosensor. The photosensors 16 and 17 can receive light fromthe optical fibers in radiation sensor 12 and generate electrical pulsesbased on the numbers of photons that they receive. The photosensors 16and 17 are electrically coupled to an electronics module 19. Theelectrical pulses can be shaped, digitized, analyzed, or any combinationthereof by the electronics module 19 to provide information regardingthe amount of light received from either or both of the photosensors 16and 17 or other information. The electronics module 19 can include anamplifier, a discriminator, an analog-to-digital signal converter, aphoton counter, another electronic component, or any combinationthereof. In an alternative embodiment (not illustrated), one of thephotosensors 16 or 17 may be replaced by a reflector. Only onephotosensor may be used with a reflector in place of the photosensor onthe other side of the detector. Analysis may also incorporate one ormore signal analysis algorithms in an application-specific integratedcircuit (“ASIC”), a field-programmable gate array (“FPGA”), or anothersimilar device.

FIG. 2 includes a cross-sectional view of a radiation sensor 10 thatincludes layers of phosphorescent material 222. In an embodiment, thematerial can include ⁶Li or ¹⁰B. In a particular embodiment, thematerial can include ⁶LiF. Another material can be capable of generatingscintillating light. The other material can include a ZnS, a CdWO₄, aY₂SiO₅, a ZnO, a ZnCdS, or any combination thereof. In anotherembodiment, the other material can include silver doped ZnS (ZnS:Ag) orcopper doped ZnS (ZnS:Cu). In a particular embodiment, the material caninclude ZnS:Ag, ZnS:Cu, ZnS:Ti, Y₂SiO₅:Ce, ZnO:Ga, ZnCdS:Cu, or anycombination thereof.

Scintillating light from the phosphorescent material 222 passes througha clear material 226 and is received by optical fibers 224. The clearmaterial can be a polymer. In one embodiment, the clear material can bean epoxy polymer. The optical fibers can have a rectangular crosssection as shown by element 224 in FIG. 2. In other embodiments thecross section of the wavelength shifting fibers can be circular, oval,or ellipsoidal. The optical fibers transmit scintillating light orderivatives of a scintillating light (not illustrated in FIG. 2). Aderivative of the scintillating light from the scintillator can be lightthat is emitted from a wavelength shifting element, such an opticalfiber containing a wavelength shifting material or member. In anembodiment, the derivative of the scintillating light has a wavelengthgreater than the wavelength of the scintillating light.

A reflector 240 surrounds the combination of the phosphorescent material222, the optical fibers 224, and the clear material 226 as illustratedin FIG. 2 to increase the amount of scintillating light received by theoptical fibers 224. In one embodiment, the scintillating light isshifted to light of a longer wavelength and transmitted to a photosensor(not illustrated in FIG. 2) that converts light received by thephotosensor to an electronic signal. Further illustrated in FIG. 2 is aneutron moderator 260 that converts fast neutrons to thermal neutrons toincrease the likelihood of capture of a neutron by the phosphorescentmaterial 222. The radiation sensor 12 can be in the form of a rectangle,or any other suitable shape. The optical fibers can also include awavelength-shifting material. In an embodiment, the optical fiber canshift the wavelength of scintillating light to a longer wavelength. Forexample, the optical fiber may shift the wavelength to blue light orgreen light

In an embodiment, optical fibers in a radiation sensor can be heldtogether by a binder. In another embodiment, the optical fibers can beheld together mechanically. The optical fibers may be arranged in anarray of rows and columns or an irregular pattern, for example, not anarray of rows and columns. The optical fibers can be in the form of aclosely packed bundle, wherein a majority of the optical fibers 224contact at least three other fibers. The space between fibers can beoccupied at least part with a binder.

The optical fibers can include optical cores and some or all of theoptical cores may be surrounded by a cladding or other coating having adifferent refractive index as compared to the optical core, wherein suchcladding or other coating can improve signal transmission. The opticalcores can include a polymer. The polymer can include a polyacrylate,such as polymethylmethacrylate (“PMMA”); a polystyrene; apolyvinyltoluene; or another suitable light-transmitting polymer. In aparticular embodiment, the optical core includes polystyrene. In yetanother particular embodiment, the optical core is substantially free ofpolyacrylate. In another embodiment, a layer including PMMA can surroundan optical core that includes polystyrene.

In one embodiment, the optical fiber includes a scintillation quencher.A scintillation quencher can include a material that inhibitsscintillation by absorbing radiation or particles that causescintillation in a material. In an embodiment, gamma rays or secondaryparticles can transmit along the optical fiber that contains ascintillation quencher in form of a scintillation resistant material.The scintillation resistant material can be a material such as a polymerthat includes moieties capable of substantially preventing undesiredscintillation. Alternatively or in combination with the scintillationresistant material, the scintillation quencher can include a materialthat inhibits scintillation by absorbing radiation created by undesiredscintillation. The undesired scintillation can originated fromscintillation-causing radiation, such as gamma rays or secondaryparticles. When such radiation is absorbed by a material in an opticalfiber, it may generate UV-radiation that can be absorbed by UV-absorbersthat serve as scintillation quencher without significantly interferingwith the scintillating light from a radiation detector.

Some particular types of neutron detectors generate secondary particles,such as secondary particle electrons that can interfere with thedetection of neutron. Secondary particle electrons are particlesgenerated as ionization products. They are called “secondary” becausethey are generated by other radiation (the primary radiation). Thisprimary radiation can be in the form of ions, electrons, or photons withsufficiently high energy that exceeds the ionization potential of anatom or molecule that absorbs the primary radiation. The secondaryparticles can cause undesired scintillation when absorbed by thematerial in the optical fiber. Moreover, secondary electrons cangenerate Cherenkov radiation.

Cherenkov radiation is electromagnetic radiation emitted when a chargedparticle, such as an electron, passes through a dielectric medium at aspeed greater than the phase velocity of light in that medium. Thecharged particles can polarize the molecules of that medium, which thenturn back rapidly to their ground state, emitting radiation in theprocess. The characteristic blue glow of nuclear reactors is due toCherenkov radiation.

In one embodiment, a scintillation quencher can absorb gamma radiation,secondary particles, or Cherenkov radiation. This material does notsignificantly interfere with the scintillation radiation generated whencapturing a neuron within the neutron detector.

The electromagnetic spectrum of ultraviolet light can be subdivided in anumber of ways. Ultraviolet A (“UVA”) ranges from 400 nm to 315 nm;Ultraviolet B (“UVB”) ranges from 315 nm to 280 nm; and Ultraviolet C(“UVC”) ranges from 280 nm to 100 nm. Another description of the UVspectrum includes Near UV ranging from 400 nm to 300 nm, Middle UVranging from 300 nm to 200 nm, Far UV ranging 200 nm to 122 nm, VacuumUV 200 nm to 100 nm, Low UV ranging from 100 nm to 88 nm, or Super UVranging from 150 nm to 10 nm.

Scintillation quenchers include materials that absorb partially orcompletely UV radiation. Scintillation quenchers can be UVA absorbers,UVB absorbers, or both. In one embodiment, a UV absorber is an aromaticcompound. In another embodiment, a UV absorber can include a ketone orester moiety. In one embodiment, a UV absorber is non-fluorescent or donot fluoresce at wavelengths within 25 nm of the wavelengthcorresponding to the emission maximum of the scintillating light fromthe scintillator or a derivative thereof (for example, wavelengthshifted light).

In an embodiment, the UV absorber is benzophenone or a benzophenone-likecompound, such as 2,4-dihydroxybenzophenone,2,2′,4,4′-tetrahydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone,2,2′-dihydroxy-4,4′-dimethoxybenzophenone,5-chloro-2-hydroxybenzophenone, and2,2′-dihydroxy-4-methoxybenzophenone.

In another embodiment, the UV absorber can be naphthalene or anaphthalene-like compound. In yet another embodiment, the UV absorbercan be dibenzoylmethane or a dibenzoylmethane-like compound.Alternatively, the UV absorber may have the chemical structure of, or bea compound similar to bis-ethylhexyloxyphenol methoxyphenyl triazine,butyl methoxydibenzoylmethane; diethylamino hydroxybenzoyl hexylbenzoate, methylene bis-benzotriazolyl tetramethylbutylphenol, methylanthranilate, ethylhexyl methoxycinnamate, ethylhexyl salicylate,ethylhexyl triazone, ethylhexyl dimethyl benzoic acid, homomethylsalicylate, is amyl p-methoxycinnamate, octocrylene; butyloctylsalicylate, diethylhexyl 2,6-naphthalate, or diethylhexyl syringylidenemalamute. In yet another embodiment, the scintillation quencher issubstantially free of nitrogen.

In yet another embodiment, the UV absorber includes a mixture of UVabsorbing compounds. In one particular embodiment, the UV absorberabsorbs light at wavelength less than 420 nm. In another particularembodiment, the UV absorber absorbs Cherenkov light.

In another embodiment, the scintillation quencher can include ascintillation resistant material. The scintillation resistant materialcan be a polymer including a UV absorber. The UV absorber can beincorporated into the polymer matrix. The UV absorber can be covalentlybonded to the matrix. For example, the UV absorber can include a monomerhaving a UV-absorbing moiety which will be incorporated into thepolymeric chain upon curing or polymerization. Such monomericUV-absorbing units can be derivatives of aromatic ketones, such asbenzophenones or dibenzoylmethanes, which contain an additional vinylgroup as a chain-forming unit upon curing or polymerization.

In embodiments, the scintillation quencher is present in the opticalfiber in an amount of at least about 50 ppm by weight, at least about129 ppm by weight, at least about 0.01% by weight, at least about 0.05%by weight, at least about 0.5% by weight, or even at least about 1.0% byweight. In other embodiments, the scintillation quencher is in amountsnot greater than about 10.0% by weight, or not greater than about 5.0%by weight, such as not greater than about 3.0% by weight, not greaterthan about 0.9% by weight, or not greater than 0.1% by weight. Further,in other embodiments, the optical fiber includes a wavelength-shiftingmaterial.

A radiation sensor or a radiation detecting system containing ascintillation quencher can have reduced likelihood of incorrectlyidentifying gamma radiation as a neutron than a radiation sensor orradiation detector that lacks a scintillation quencher. Referring toFIG. 4, a pulse shape discrimination spectrum illustrates counts as afunction of channel number of a multi-channel analyzer for a neutronsource, such as ²⁴¹AmBe, ²⁵²Cf, ²³⁹PuBe, or the like. In the embodimentcorresponding to FIG. 4, when significant gamma radiation is notpresent, the spectrum 40 for a neutron source has a relatively high,sharp peak at a lower channel number, a relatively broader peak at ahigher number, and a valley between the peaks.

In FIG. 4, a couple of dashed lines are illustrated as starting from thenear the bottom of the valley, wherein a dashed line 44 corresponds toonly gamma radiation received by the radiation detecting system with thescintillation quencher, and a dashed line 42 that corresponds to onlygamma radiation received by the radiation detecting system without thescintillation quencher. The dashed line 44 is steeper than the dashedline 42. Thus, the radiation detecting system with the scintillationquencher has significantly lower amounts of gamma radiation at channelnumbers greater than the channel number corresponding to the bottom ofthe valley, as compared to a corresponding radiation detecting systemwithout the scintillation quencher.

The probability of incorrectly identifying gamma radiation as a neutroncount is roughly proportional to the area under the curve defined by thedashed line 42 or 44 and to a line corresponding to the channel numberof the discrimination setting. Referring to FIG. 4, when thediscrimination setting is at about channel number 96 (line 47), the areaunder the curve for the dashed line 44 is significantly smaller than thearea under the curve for the dashed line 42. When the discriminationsetting is increased to about channel number 168 (line 45), the areaunder the curve for the dashed line 44 is below 1 count while the areaunder the curve for the dashed line 42 remains significant. Thus, thelikelihood of incorrectly identifying gamma radiation as a neutron canbe reduced by factor at least about 1.5, at least about 2, at leastabout 5, at least about 11, or even at least about 101 compared to acorresponding radiation detecting system that does not have ascintillation quencher.

The significance of the scintillation quencher may be more apparent whenconsidered in the presence of a significant gamma field and in thecontext of setting a discrimination level for pulse shapediscrimination. A significant gamma field may be about 10 mR/hour, about20 mR/hour, or another value produced by a gamma radiation source, suchas ²²Na, ⁶⁰Co, ¹³⁷Cs, or the like. In a particular embodiment, a gammaradiation source may be placed at an appropriate distance from theradiation sensor, such that the radiation sensor is exposed to thedesired gamma radiation field.

FIG. 5 includes pulse shape discrimination spectra for the neutronsource and the gamma radiation source, wherein the radiation sensor isexposed to about 10 mR/hour of gamma radiation. The spectrum 40corresponds to the neutron source that has been previously described.The spectra for the radiation detecting systems can be different for thesignificant gamma radiation field. For both radiation detecting systems,the counts rise quickly at low channel numbers, and, thus, the rise forboth spectra are illustrated by dashed line 51. At higher channelnumbers, the dashed line 54 corresponds to gamma radiation from thegamma radiation source as received by the radiation detecting systemwith the scintillation quencher, and the dashed line 52 corresponds togamma radiation from the gamma radiation source received by acorresponding radiation detecting system without the scintillationquencher. Dashed line 54 is steeper than the dashed line 52.

For the radiation detecting system with the scintillation quencher, thediscrimination setting may be set to about channel number 161 (line 57in FIG. 5). When the discrimination setting is at channel number 161,the radiation detecting system can detect neutrons at channel number 161and higher. If the likelihood of incorrectly detecting gamma radiationas a neutron is not to be increased, the corresponding radiationdetecting system without a scintillation quencher may have thediscrimination setting increased to about channel number 258 (line 55).When the discrimination setting is at channel number 258, thecorresponding radiation detecting system can detect neutrons only atchannel number 258 and higher. Note that channel number 258 is close tothe channel number corresponding to the highest count for the broaderpeak of the spectrum 40. Therefore, a substantial portion of spectrum 40will not be analyzed for neutrons due to an unacceptably high likelihoodof incorrectly detecting gamma radiation as a neutron. Unlike thecorresponding radiation detecting system, the radiation detecting systemwith the scintillation quencher can detect neutrons over a substantiallylarger range of channel numbers. In the embodiment corresponding to FIG.5, the radiation detecting system with the scintillation quencher candetect neutrons at channel numbers in a range of 161 to 257, which isoutside the range for the corresponding radiation detecting system.

As compared to the corresponding radiation detecting system, theradiation detecting system with the scintillation quencher can detectneutrons at lower channel numbers, and at a particular discriminationsetting is less likely to incorrectly identify gamma radiation as aneutron. Therefore, the radiation detecting system with thescintillation quencher provides for more accurate neutron detection ascompared to the corresponding radiation detecting system at a relativelylow gamma radiation field, a relatively high gamma radiation field, orboth. Thus, the corresponding radiation detecting system is at leastabout 1.5, at least about 2, at least about 5, at least about 11, or atleast about 101 times more likely to incorrectly identifying gammaradiation as a neutron as compared to the radiation detecting systemwith the scintillation quencher.

In an embodiment, the optical fiber has a circular cross section havinga diameter of at least about 0.5 mm, such as about 0.8 mm, about 1.0 mm,or about 1.5 mm. The diameter of the optical fiber is not greater thanabout 3 mm, such as about 2.5 mm, or about 2.0 mm. In anotherembodiment, the optical fiber has a rectangular cross section, with adiagonal length of at least about 0.5 mm, such as about 0.8 mm, about1.0 mm, or about 1.5 mm. The diagonal length of the optical fiber is notgreater than about 3 mm, such as about 2.5 mm, or about 2.0 mm.

The radiation detection apparatus can be a medical imaging apparatus, awell logging apparatus, a security inspection apparatus, or the like. Asillustrated in FIG. 3, the radiation detection apparatus 502 can be usedas a security inspection apparatus. The radiation detection apparatus502 can include one or more radiation sensors and photosensorarrangements (not separately illustrated in FIG. 3) as described herein.The radiation sensor(s) can be of any of the previously describedradiation sensors. As illustrated in FIG. 3, the radiation sensor(s) maybe located within either or both of the vertical columns, the horizontalcross member, or any combination thereof.

When in use, an object 504 can be placed near or pass through an openingwithin radiation detection apparatus 502. As illustrated in theembodiment of FIG. 3, the object 504 is a vehicle, and in particular, atruck. The radiation detection apparatus 502 can capture at least partof the targeted radiation emitted by the object 504. The radiationsensors can emit scintillating light or wavelength shifted light that isconverted to an electronic signal by the photosensors. The electronicsignal can be transmitted to a control module (not illustrated) forfurther analysis.

Other embodiments do not require a dedicated neutron moderator tosurround an arrangement of optical fibers. The optical fibers caninclude a material that is capable of converting fast neutrons tothermal neutrons. When the optical fibers are arranged to an appropriatethickness, fast neutrons can be converted to thermal neutrons andcaptured by the phosphorescent material. During manufacturing, anoperation to place a neutron moderator around the optical fibers is notneeded, thus, saving production time and potential yield losses or otherdefects associated with performing operations that are not required.

Embodiments as described herein can help to reduce radiation other thanthe neutron capture, such as gamma radiation-caused scintillation, orelectron or secondary electron-caused scintillation, both of which canoccur in the polymer matrix of the optical fiber. For example, in aneutron detector, scintillation from capturing a neutron contributes toa signal that is desired, whereas scintillation from any other event,for example, gamma radiation or secondary particle, contributes tonoise, and the noise may interfere with the detection of or the analysisof the signal. Hence, a higher signal-to-noise ratio can provide moreaccurate readings. Thus, the radiation sensors and apparatuses asdescribed using the concepts herein provide signal-to-noise ratios thanconventional radiation sensors and apparatuses configured to sense anddetect neutrons. In particular embodiments, radiation detectionapparatuses and components as described herein may be more sensitive toneutrons, less sensitive to gamma radiation, or any combination thereof.

Unlike the radiation detection apparatuses and components as describedherein, a high energy particle counter may employ wavelength shiftingsheets of polyvinyltoluene that include benzophenone. A high energyparticle counter is typically determining the total energy fromparticles. Thus, high energy particle counters are not concerned withcorrectly counting neutrons in the presence of gamma radiation and othersources that significantly interfere with correctly counting theneutrons.

Further, the sheet of polyvinyltoluene may have issues with opticallycoupling to a tube-shaped photosensor, which is commonly used withradiation sensors that are to sense neutrons. If a tube-shapedphotosensor would be used, significant signal loss would occur in thetransition between the edge of the sheet and the photosensor. Such aconfiguration may not be able to provide a sufficiently intense signalto the photosensor and cause undercounting of neutrons.

Still further, polyvinyltoluene may not be able to be formed intooptical fibers of a size and shape that works well with radiationsensors that are to sense neutrons. For example, a radiation sensor mayinclude many optical fibers that cover a relatively large radiationsensing area, yet outside the radiation sensing area, the optical fibersmay include bends and be bundled together, so that the optical fibersare sufficiently optically coupled to a photosensor. Optical fibers madewith a polyvinyltoluene core exhibit poorer signal transmission thancomparable fibers made with a polystyrene core. Furthermore, it is moredifficult to draw polyvinyltoluene fibers as the material tends to bindor clump rather than smoothly transition to a consistent size.

Accordingly, the optical fibers are described herein, particularly whenincorporated into a radiation sensor, overcome many of the shortcomingsof polyvinyl toluene sheets, and particularly for use of the opticalfibers in a neutron sensor. A radiation detection apparatus having aradiation sensor with optical fibers as described herein can have arelatively high signal:noise ratio, and in particular, improved accuracyto detect neutrons even when other radiation, such as gamma radiation,is present. Thus, analysis of the output from the photosensor canprovide better discrimination of neutrons from gamma radiation.

Many different aspects and embodiments are possible. Some of thoseaspects and embodiments are described herein. After reading thisspecification, skilled artisans will appreciate that those aspects andembodiments are only illustrative and do not limit the scope of thepresent invention. Additionally, those skilled in the art willunderstand that some embodiments that include analog circuits can besimilarly implemented using digital circuits, and vice versa.

In a first aspect, a radiation sensor can include a scintillator and anoptical fiber coupled to the scintillator, wherein the optical fiberincludes a scintillation quencher.

In an embodiment of the first aspect, the scintillation quencherincludes a UV-absorber. In a particular embodiment, the UV-absorberabsorbs radiation at wavelengths in a UV-A range, in a UV-B range, in aUV-C range, or any combination thereof. In a particular embodiment ofany of the preceding embodiments, the scintillation quencher absorbsCherenkov light. In another particular embodiment of any of thepreceding embodiments, the scintillation quencher includes ascintillation resistant material. In still another particular embodimentof any of the preceding embodiments, the scintillator is capable ofgenerating a first radiation having a wavelength of at least about 420nm, and the scintillation quencher is capable of absorbing a secondradiation having a wavelength of less than about 420 nm.

In a further particular embodiment of any of the preceding embodiments,the scintillation quencher is selected from the group consisting ofaromatic compounds, ketones, and esters. In still a further particularembodiment of any of the preceding embodiments, the scintillationquencher is substantially free of nitrogen. In yet a further particularembodiment of any of the preceding embodiments, the scintillationquencher is selected from the group consisting of benzophenones. In amore particular embodiment, the scintillation quencher is selected frombenzophenone, 2,4-dihydroxybenzophenone,2,2′,4,4′-tetrahydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone,2,2′-dihydroxy-4,4′-dimethoxybenzophenone,5-chloro-2-hydroxybenzophenone, and2,2′-dihydroxy-4-methoxybenzophenone. In another particular embodimentof any of the preceding embodiments, the scintillation quencher ispresent in the optical fiber in an amount of at least about 50 ppm byweight, at least about 129 ppm by weight, at least about 0.01% byweight, at least about 0.05%, of at least about 0.5%, of at least about1.0%. In still another particular embodiment of any of the precedingembodiments, the scintillation quencher is present in the optical fiberin an amount not greater than about 5.0% by weight, not greater thanabout 3.0% by weight, not greater than about 0.9% by weight, or notgreater than about 0.1% by weight.

In a further particular embodiment of any of the preceding embodiments,the optical fiber further includes a wavelength shifting material. Instill a further particular embodiment of any of the precedingembodiments, the optical fiber includes a polymer. In a more particularembodiment, the polymer includes a polystyrene. In still another moreparticular embodiment, the polymer is substantially free of apolyacrylate. In yet a further particular embodiment of any of thepreceding embodiments, the radiation sensor includes a neutron sensor.

In a second aspect, a radiation detecting system can include ascintillator, a photosensor, and an optical fiber coupled between thescintillator and the photosensor. The optical fiber can include ascintillation quencher and operates at a higher signal-to-noise ratiothan another optical fiber that does not include any scintillationquencher.

In an embodiment of the second aspect, the photosensor has a sensitivityfor radiation in a wavelength between 350 nm and 600 nm. In a particularembodiment, the photosensor has a sensitivity for radiation in awavelength between 400 nm and 500 nm. In a particular embodiment of anyof the preceding embodiments of the second aspect, the scintillationquencher includes a scintillation resistant material. In anotherparticular embodiment of any of the preceding embodiments of the secondaspect, the scintillation quencher includes a UV-absorber. In stillanother particular embodiment of any of the preceding embodiments of thesecond aspect, the scintillation quencher absorbs radiation atwavelengths in a UV-A range, in a UV-B range, in a UV-C range, or anycombination thereof. In yet another particular embodiment of any of thepreceding embodiments of the second aspect, the scintillation quencherabsorbs Cherenkov light. In a further particular embodiment of any ofthe preceding embodiments of the second aspect, the scintillator iscapable of generating a first radiation having a wavelength of at leastabout 420 nm, and the scintillation quencher is capable of absorbing asecond radiation having a wavelength of less than about 420 nm.

In still a further particular embodiment of any of the precedingembodiments of the second aspect, the scintillation quencher is selectedfrom the group consisting of aromatic compounds, ketones, and esters. Inyet a further particular embodiment of any of the preceding embodimentsof the second aspect, the scintillation quencher is substantially freeof nitrogen. In another particular embodiment of any of the precedingembodiments of the second aspect, the scintillation quencher is selectedfrom the group consisting of benzophenones. In a more particularembodiment of any of the preceding embodiments of the second aspect, thescintillation quencher is selected from benzophenone,2,4-dihydroxybenzophenone, 2,2′,4,4′-tetrahydroxybenzophenone,2-hydroxy-4-methoxybenzophenone,2,2′-dihydroxy-4,4′-dimethoxybenzophenone,5-chloro-2-hydroxybenzophenone, and2,2′-dihydroxy-4-methoxybenzophenone. In still another particularembodiment of any of the preceding embodiments of the second aspect, thescintillation quencher is present in the optical fiber in an amount ofat least about 50 ppm by weight, at least about 129 ppm by weight, atleast about 0.01% by weight, at least about 0.05%, of at least about0.5%, or at least about 1.0%. In yet another particular embodiment ofany of the preceding embodiments of the second aspect, the scintillationquencher is present in the optical fiber in an amount not greater thanabout 5.0% by weight, not greater than about 3.0% by weight, not greaterthan about 0.9% by weight, or not greater than about 0.1% by weight.

In a particular embodiment of any of the preceding embodiments of thesecond aspect, the optical fiber further includes a wavelength shiftingmaterial. In another particular embodiment of any of the precedingembodiments of the second aspect, the optical fiber includes of apolymer. In still another particular embodiment of any of the precedingembodiments of the second aspect, the polymer includes a polystyrene. Ina more particular embodiment, the polymer is substantially free of apolyacrylate. In yet another particular embodiment of any of thepreceding embodiments of the second aspect, the radiation sensorincludes a neutron sensor.

In a third aspect, an optical fiber can include a polymer core, and ascintillation quencher.

In an embodiment of the third aspect, the optical fiber further includesa wavelength shifting material. In a particular embodiment of any of thepreceding embodiments of the third aspect, the polymer core includes apolystyrene. In another particular embodiment of any of the precedingembodiments of the third aspect, the scintillation quencher includes aUV-absorber. In a more particular embodiment, the UV-absorber absorbsradiation at wavelengths in a UV-A range, in a UV-B range, in a UV-Crange, or any combination thereof. In still another particularembodiment of any of the preceding embodiments of the third aspect, thescintillation quencher absorbs Cherenkov light. In yet anotherparticular embodiment of any of the preceding embodiments of the thirdaspect, the scintillation quencher includes a scintillation resistantmaterial. In a further particular embodiment of any of the precedingembodiments of the third aspect, the optical fiber is capable oftransmitting a first radiation having a wavelength of at least about 420nm, and the scintillation quencher is capable of absorbing a secondradiation having a wavelength of less than about 420 nm.

In still a further particular embodiment of any of the precedingembodiments of the third aspect, the scintillation quencher is selectedfrom the group consisting of aromatic compounds, ketones, and esters. Inyet a further particular embodiment of any of the preceding embodimentsof the third aspect, the scintillation quencher is substantially free ofnitrogen. In a particular embodiment of any of the preceding embodimentsof the third aspect, the scintillation quencher is selected from thegroup consisting of benzophenones. In a more particular embodiment, thescintillation quencher is selected from benzophenone,2,4-dihydroxybenzophenone, 2,2′,4,4′-tetrahydroxybenzophenone,2-hydroxy-4-methoxybenzophenone,2,2′-dihydroxy-4,4′-dimethoxybenzophenone,5-chloro-2-hydroxybenzophenone, and2,2′-dihydroxy-4-methoxybenzophenone. In another particular embodimentof any of the preceding embodiments of the third aspect, thescintillation quencher is present in the optical fiber in an amount ofat least about 50 ppm by weight, at least about 129 ppm by weight, atleast about 0.01% by weight, at least about 0.05%, of at least about0.5%, of at least about 1.0%. In still another particular embodiment ofany of the preceding embodiments of the third aspect, the scintillationquencher is present in the optical fiber in an amount not greater thanabout 5.0% by weight, not greater than about 3.0% by weight, not greaterthan about 0.9% by weight, or not great than about 0.1% by weight.

In a further particular embodiment of any of the preceding embodimentsof the third aspect, the optical fiber has a circular cross section witha diameter of at least about 0.5 mm, at least about 0.8 mm, or at leastabout 1.0 mm. In another further particular embodiment of any of thepreceding embodiments of the third aspect, the optical fiber has acircular cross section with a diameter not greater than about 3.0 mm,not greater than about 2.5 mm, or not greater than about 2.0 mm. In yetanother particular embodiment of any of nearly all of the precedingembodiments of the third aspect, the optical fiber has a rectangularcross section with a diagonal length of at least about 0.5 mm, at leastabout 0.8 mm, or at least about 1.0 mm. In still another particularembodiment of any of nearly all of the preceding embodiments of thethird aspect, the optical fiber has a rectangular cross section with adiagonal length not greater than about 3.0 mm, not greater than about2.5 mm, or not greater than about 2.0 mm.

In a fourth aspect, a method to detect a neutron can include providing ascintillator coupled to an optical fiber, wherein the optical fiberincludes a scintillation quencher. The method can also include emittinga first radiation in the scintillator and transmitting the firstradiation along the optical fiber. The method can further includequenching a second radiation in the optical fiber, wherein the firstradiation is different from the second radiation.

In an embodiment of the fourth aspect, the method further includesreceiving at a photosensor the first radiation or a derivative of thefirst radiation, wherein a radiation detecting system includes thescintillator, the optical fiber, and the photosensor. In a particularembodiment, a signal-to-noise ratio with the radiation detecting systemis higher than a signal-to-noise ratio with a corresponding radiationdetecting system without the scintillation quencher.

In another particular embodiment of any of the preceding embodiments ofthe fourth aspect, the second radiation is Cherenkov light. In stillanother particular embodiment of any of the preceding embodiments of thefourth aspect, the first radiation has a wavelength of at least about420 nm. In yet another particular embodiment of any of the precedingembodiments of the fourth aspect, the method further includes quenchinga third radiation, wherein the third radiation is scintillation lightgenerated in the optical fiber. In a further particular embodiment ofany of the preceding embodiments of the fourth aspect, the methodfurther includes quenching a fourth radiation, wherein the fourthradiation is light passing along the optical fiber, the light having awavelength of less than 420 nm. In another further particular embodimentof any of the preceding embodiments of the fourth aspect, acorresponding radiation detecting system without the scintillationquencher is at least about 1.5, at least about 2, at least about 5, atleast about 11, or at least about 101 times more likely to incorrectlyidentifying gamma radiation as a neutron as compared to the radiationdetecting system with the scintillation quencher. In a more particularembodiment, the method can include exposing the radiation detectingsystem with the scintillation quencher and the corresponding radiationdetecting system to a gamma radiation field of at least about 10 mR/houror at least about 20 mR/hour.

In still another further particular embodiment of any of the precedingembodiments of the fourth aspect, the scintillation quencher is selectedfrom the group consisting of aromatic compounds, ketones, and esters. Inyet another further particular embodiment of any of the precedingembodiments of the fourth aspect, the scintillation quencher issubstantially free of nitrogen. In a particular embodiment of any of thepreceding embodiments of the fourth aspect, the scintillation quencheris selected from the group consisting of benzophenones. In a moreparticular embodiment, the scintillation quencher is selected frombenzophenone, 2,4-dihydroxybenzophenone,2,2′,4,4′-tetrahydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone,2,2′-dihydroxy-4,4′-dimethoxybenzophenone,5-chloro-2-hydroxybenzophenone, and2,2′-dihydroxy-4-methoxybenzophenone. In another particular embodimentof any of the preceding embodiments of the fourth aspect, the methodfurther includes shifting the first radiation to a higher wavelength toform a derivative of the first radiation along the optical fiber.

The radiation sensor, the radiation detecting system, or the method ofany one of the preceding claims, wherein optical fibers are wavelengthshifting fibers that include polystyrene, and the scintillation quencheror scintillation resistant material includes benzophenone.

Note that not all of the activities described above in the generaldescription or the examples are required, that a portion of a specificactivity may not be required, and that one or more further activitiesmay be performed in addition to those described. Still further, theorder in which activities are listed is not necessarily the order inwhich they are performed.

Certain features that are, for clarity, described herein in the contextof separate embodiments, may also be provided in combination in a singleembodiment. Conversely, various features that are, for brevity,described in the context of a single embodiment, may also be providedseparately or in any subcombination. Further, reference to values statedin ranges includes each and every value within that range.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any feature(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature of any or all the claims.

What is claimed is:
 1. An optical fiber, comprising: a polymer core; a wavelength-shifting material; and a scintillation quencher including a UV-absorber, wherein the scintillation quencher is selected from a group consisting of benzophenone, 2,4-dihydroxybenzophenone, 2,2′,4,4′-tetrahydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, 5-chloro-2-hydroxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone, or a combination thereof.
 2. The optical fiber according to claim 1, wherein the polymer core comprises a polystyrene.
 3. The optical fiber according to claim 1, wherein the optical fiber comprises a cladding.
 4. The optical fiber according to claim 1, wherein the UV-absorber absorbs radiation at wavelengths in a UV-A range, in a UV-B range, in a UV-C range, or any combination thereof.
 5. The optical fiber according to claim 1, wherein the scintillation quencher absorbs Cherenkov light.
 6. The optical fiber according to claim 1, wherein the scintillation quencher includes a scintillation resistant material.
 7. The optical fiber according to claim 1, wherein: the optical fiber is capable of transmitting a first radiation having a wavelength of at least about 420 nm; and the scintillation quencher is capable of absorbing a second radiation having a wavelength of less than about 420 nm.
 8. The optical fiber according to claim 1, wherein the scintillation quencher is in an amount of at least about 50 ppm by weight and no greater than about 10.0% by weight.
 9. The optical fiber according to claim 1, wherein the optical fiber has a circular cross section with a diameter of at least about 0.5 mm to not greater than about 3.0 mm.
 10. The optical fiber according to claim 1, wherein the optical fiber has a rectangular cross section with a diagonal length of at least about 0.5 mm to not greater than about 3.0 mm.
 11. A radiation sensor, comprising: a scintillator; and the optical fiber according to claim 1, wherein the optical fiber is coupled to the scintillator.
 12. The radiation sensor according to claim 11, wherein the scintillator is capable of generating a first radiation having a first wavelength of at least about 420 nm, and the scintillator quencher is capable of absorbing a second wavelength of less than about 420 nm.
 13. A radiation detecting system, comprising: a scintillator; a photosensor; and the optical fiber according to claim 1, wherein the optical fiber is coupled between the scintillator and the photosensor.
 14. An optical fiber, comprising: a polymer core; and a scintillation quencher in an amount of at least about 50 ppm by weight and no greater than about 10.0% by weight.
 15. The optical fiber according to claim 14, wherein the scintillation quencher includes a scintillation resistant material.
 16. The optical fiber according to claim 14, wherein the scintillation quencher is substantially free of nitrogen.
 17. The optical fiber according to claim 14, wherein the scintillation quencher is selected from a group consisting of benzophenones.
 18. The optical fiber according to claim 14, further comprising a wavelength shifting material.
 19. The optical fiber according to claimed 14, wherein the scintillation quencher comprises a UV-absorber.
 20. The optical fiber according to claimed 19, wherein the UV-absorber absorbs radiation at wavelengths in a UV-A range, in a UV-B range, in a UV-C range, or any combination thereof. 